1. The Field of the Invention
This invention relates to a system for treating air for supply to an enclosed space in which it is to be breathed.
2. The Relevant Technology
It can be desirable to treat air that is to be breathed to remove contaminants and also to provide a suitable proportion of the individual components of an air mixture (oxygen, carbon dioxide, nitrogen etc). Contaminants that are to be removed might be solid (in particulate form), liquid (in aerosol form) or gaseous. The enclosed space in which the treated air is to be breathed might be a building or a vehicle. An example of an application for the system of the invention might be for example in an agricultural vehicle which can be exposed to an environment containing particulate and liquid or gaseous materials which preferably the driver of the vehicle should not be exposed to.
It is known to remove contaminants from a gas using regenerative adsorption apparatus. Such apparatus comprises at least two chambers, each containing a quantity of an adsorbent material. The gas is directed to flow through one of the chambers so that it can be treated while the adsorbent material in the other chamber is regenerated by displacement from it of the contaminant material which has previously been adsorbed while pressure in that chamber is reduced. The adsorbed component can be displaced by means of a purge stream of gas which might be taken from the outlet stream from the chamber in which adsorption is taking place. The regeneration of the adsorbent material can involve changes in one or both of the pressure and temperature in the chamber, especially a reduction in the pressure in the chamber and an increase in the temperature.
It is a disadvantage of known regenerative adsorption assemblies that large chambers can be required in order to provide sufficient adsorbent material to treat enough air adequately for it to be breathed, especially when the contaminants in the air only bond loosely to the adsorbent material
According to the present invention, a system for treating air for supply to an enclosed space includes a regenerative adsorption assembly and a recirculation path for supplying breathed air from the enclosed space to be mixed with air from atmosphere before it is supplied to the enclosed space
Accordingly, in one aspect, the invention provides a system for treating air for supply to an enclosed space in which it is to be breathed, which comprises:
a. an inlet through which air can enter the system from atmosphere for supply to the enclosed space;
b. a regenerative adsorption assembly comprising at least two chambers which contain an adsorbent material, arranged so that air flowing in the inlet for supply to the enclosed space can pass through one of the chambers for adsorption of contaminants before supply to the enclosed space while adsorbent material in another of the chambers is purged of adsorbed contaminants;
c. a recirculation path for supplying air from the enclosed space to the inlet to be mixed with air from atmosphere before it is supplied to the enclosed space; and
d. means for adjusting the resistance to flow of air through the recirculation path according to the resistance that is provided to the flow of air from atmosphere into the enclosed space.
The system of the invention has the advantage that the load on the adsorbent material from contaminants in air which enters the system from the atmosphere is reduced so that adequate adsorption of the contaminants in air is possible with chambers for the adsorbent material in the pressure swing adsorption assembly which are smaller than are required conventionally without the recirculation path feature of the system.
The provision of means for adjusting the resistance to flow of gas through the recirculation path can ensure that the recirculated air and atmospheric air can be mixed in a desired ratio by allowing increased flow of recirculated air when the resistance to flow of atmospheric air is increased. Such an increase in the resistance to flow of atmospheric air can result from an increase in the air flow that is admitted to the enclosed space through one of the chambers which contain adsorbent material.
The resistance to flow of gas through the recirculation path can be adjusted by means of a variable flow restrictor. Such a component can be driven by an electrical motor in response to signals from control components. Preferably, however, the flow resistance is varied by provision of two or more recirculation paths which present different resistances to flow of gas through them, the system including means for changing the recirculation path through which the recirculated gas flows. For example, the system can provide two recirculation paths. One of them can provide little or no resistance to flow of air for use when air flows directly into the enclosed space and does not pass through the adsorption assembly. The other recirculation path provides greater resistance to flow of air for use when air flows into the enclosed space after flowing through the adsorption assembly. The selection of the recirculation path for the air can be made using appropriate valves which can be controlled by signals from control components.
In another aspect, the invention provides a method of treating air for supply to an enclosed space in which it is to be breathed, which comprises:
a. admitting air to an air treatment system from atmosphere;
b. mixing the air from atmosphere with recirculated air from the enclosed space;
c. passing the mixture through a chamber of a regenerative adsorption assembly comprising at least two such chambers, each containing an adsorbent material for adsorption of contaminants; and
d. supplying the air from the chamber after it has passed over the adsorbent material to the enclosed space.
Preferably, the system includes means for adjusting the relative proportions of the air from atmosphere and the air that is recirculated from the enclosed space that are mixed before supply to the enclosed space. This allows the extent of the treatment of the air that is supplied to the enclosed space to be adjusted according to the amount of contamination that is in the atmospheric air. For example, atmospheric air that is relatively clean and which only requires moderate treatment (if any) can be supplied to the enclosed space with little or no recirculated air. When the atmospheric air contains significant quantities of contaminant material, it will be supplied to the enclosed space with relatively more recirculated air, for example, so that the air that is supplied to the enclosed space comprises at least 40% recirculated air, and possibly at least 50% or at least 60% or more. The availability of recirculated air means that the load placed on the adsorbent material in the chambers need not become too high, even when atmospheric air contains high concentrations of contaminant material.
The means for adjusting the relative proportions of atmospheric and recirculated air can comprise a valve. The valve preferably provides constrictions against flow of the air from atmosphere and of the recirculated air, with the size of the at least one of the constrictions being variable. The valve makes it possible for the air from atmosphere and from the enclosed space to mix, notwithstanding the possibility that the air in the enclosed space is at a higher pressure than the air from atmosphere. Preferably, the valve considered as a whole amounts to a 3:2 valve with two inlet ports for the atmospheric and recirculated air, and an outlet port for the mixed air. Preferably, the valve is capable of closing completely the path for air to flow from atmosphere directly into the enclosed space, for example, in the event that there is an unexpected drop in air pressure within the enclosed space so that the pressure there is less than atmospheric pressure.
Preferably, the system includes a by-pass line for air from atmosphere to flow past the regenerative adsorption assembly when the air from atmosphere contains little or no contaminants. When air is supplied to the enclosed space directly from atmosphere, the system can be operated without recirculation of air from the enclosed space so that the air that is supplied to the enclosed space consists entirely of air from atmosphere. The resistance to flow of the recirculated gas can be adjusted to take into account the variation in the resistance to flow of gas entering the enclosed space.
The system will generally include a blower for forcing air into the enclosed space to maintain it at a pressure that is above atmospheric pressure. Preferably, the system includes a pressure sensor for monitored the pressure within the enclosed space, the blower being adjustable according to the monitored pressure to maintain the pressure within the enclosed space below a predetermined maximum pressure. This has the advantage that a positive pressure can be maintained within the enclosed space without admitting more air to the space than is necessary for this purpose. This has the advantage that the size of the chambers of adsorbent material can be kept small.
Preferably, the system includes means for detecting contaminant material in air that is admitted to the system from atmosphere and which are not to be admitted to the enclosed space. Signals from the detection means can control a by-pass line by which air from atmosphere flows past the regenerative adsorption assembly, closing the by-pass line when contaminant material is detected. When the detection means can quantify the amount of the contaminant material in the atmospheric air, a signal from the detection means can be used to control the relative proportions of the air from atmosphere and the air that is recirculated from the enclosed space that are mixed before supply to the enclosed space.
Preferably, the regenerative adsorption assembly is arranged to provide a change in the pressure or the temperature or both in each chamber between the phase when the chamber is exposed to air that is to be treated and the phase when the adsorbent material in the chamber is regenerating. Preferably, the assembly is arranged so that the difference in pressure in each chamber between the adsorption and regeneration phases is at least about 750 mbarg, more preferably at least about 1000 mbarg, especially at least about 1500 mbarg. When the difference between pressure within a chamber in the adsorption phase and atmospheric pressure is less than the difference between the pressures in the chamber in the adsorption and regeneration phases, the assembly can include a pump for reducing the pressure in a chamber of the regenerative adsorption assembly below atmospheric pressure during regeneration of that material. Such a pump might reduce the pressure in the chamber to at least about 400 mbar below atmospheric pressure, preferably at least about 600 mbar. The pump can have other functions: for example, it can be used to draw atmospheric air into the system.
The regenerative adsorption assembly will comprise at least two chambers. Two chambers will be sufficient for many applications. However, it might be preferred for some applications to use an adsorption assembly which includes more than two chambers. This has the advantage that the air flow speed through the chambers can be reduced, giving rise to reduced resistance to air flow.
Preferably, the assembly includes means for heating the adsorbent material in a chamber of the regenerative adsorption assembly during regeneration of that material. The heat can be supplied by one or more electric heaters located within the chamber. The temperature to which the adsorbent material is heated will be selected having regard to factors which include the nature of the adsorbent material, the strength of the interactions between the adsorbent material and adsorbed contaminants, the quantity of the contaminant material that has been adsorbed, and the energy required to heat the adsorbed material. A relatively high temperature can be preferred to optimise the purge of the adsorbed material.
Preferably, the system is configured so that the air from atmosphere and the air that is recirculated from the enclosed space are mixed upstream of the regenerative adsorption assembly so that the mixed air passes through one of the chambers for adsorption of contaminants before it is supplied to the enclosed space. The treatment of the air as it passes over the adsorbent material can then include adsorption of exhaled carbon dioxide in the recirculated air as well as adsorption of contaminants in atmospheric air. It has been found that this combined adsorption is possible without an undesirable increase in the size of the chambers for the adsorbent material. Adsorbed carbon dioxide can be discharged from the system when the adsorbent material is regenerated. An acceptable air composition for breathing is then established in air that is supplied to the enclosed space from oxygen in air supplied from atmosphere.
Preferably, the system includes a purge line through which air is supplied to a chamber of the regenerative adsorption assembly in which the adsorbent material is to be regenerated, the purge line supplying air from the outlet from the chamber through which air has flowed for adsorption of contaminants. The proportion of air from the chamber which flows in the purge line is preferably not more than about 25%, especially not more than about 5%.
The system can include components for treating air that is admitted from atmosphere. For example, the system can include means for heating or cooling the air which is admitted from atmosphere. This can have the advantage that the process of adsorbing contaminants in the air can be made more efficient. The system can include means for collecting liquid droplets carried in air that enters the system from atmosphere. This can take the form of a centrifugal separator in which vanes impart a spiralling flow to the air leading to liquid droplets carried by the air being made to coalesce; such separators are known. The system can include a filter for removing particulate contaminants from air entering the system through the inlet. Suitable filter media include borosilicate glass microfibres. The system can include means for controlling the temperature or the humidity or both of the air that enters the enclosed space, for example for the comfort of persons within the space. Suitable air conditioning equipment apparatus which can be used for this purpose are well known.
The system of the invention can be used to remove materials in vapour, liquid and particulate form from air that is to be breathed. The nature of the adsorbent material will be selected according to the nature of the contaminants in the air. Examples of suitable adsorbent materials include activated carbons and molecular sieves.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.